This invention relates to a process for the production of a profile made of composite material fibers that has a half-nail-head or nail-head cross-section. The invention also relates to the device for the implementation of said process as well as the thus obtained profile.
Certain pieces made of composite material are produced from assembled fibrous reinforcement preforms, arranged in a mold and then immersed in a resin matrix.
To obtain a T shape, according to a first embodiment that is illustrated in FIG. 1, three preforms are assembled: a first preform 10 that is called an essentially flat plate, and then two other L-shaped preforms 12, 12′ that are arranged symmetrically, each of the L-shaped preforms having a first wing that is flattened against a wing of the other L-shaped preform and a second wing that is flattened against the plate 10. Since, at the junction of the wings, the L-shaped preforms 12, 12′ have a more or less significant curvature radius, there is a space 14 that has the shape of a nail head at the junction of the three preforms. In this case, this space 14 has a cross-section with a flat surface and two concave and curved surfaces.
According to another embodiment that is illustrated in FIG. 2, at least three preforms are assembled: a first preform 20 that is called a plate, essentially flat, a second preform 22 that forms the base of the T of which one edge is flattened against the plate 20, and at least a third L-shaped preform 24 whose first wing is flattened against the plate 20, whereby the other wing is flattened against the preform 22. Since, at the junction of the wings, the preform 24 has a more or less significant curvature radius, there is a space that has the shape of a half-nail head 26 at the junction of the preforms 20 to 24. In this case, this space 26 has a cross-section with two flat surfaces and a concave and curved surface.
To ensure the soundness of the material of the piece that results from proper control of the resin injection, the space 14 or 26 should be filled with fibrous reinforcements.
According to one embodiment, an operator forms pre-impregnated or powdered carbon fibers into strands so as to obtain a strand 27 with a circular cross-section. He then positions the strand 27 that is thus produced in the space 14 or 26 using, for example, an adhesive strip, and then he heats it with an iron so that said strand 27 is made integral with the other preforms.
This embodiment is not satisfactory because it does not make it possible to achieve optimized filling of the space 14 or 26, taking into account the essentially circular cross-section of the strand. The unfilled cavities promote the appearance of preferred paths of resin that disturb the filling of the mold and consequently increase the risks of greatly porous zones and/or dry zones.
According to another drawback, as illustrated in FIG. 3, the surrounding sub-preforms of the strand 27 that is used to fill the space 14 or 26 are deformed during the assembly of the preforms or during the closing of the mold, which affects the mechanical characteristics of the thus produced piece because of the undulations of the fibers.